Problem with suddenly emerging lines

As you can see in the picture suddenly in my model I see lines that are in the back of the surface partly visible inside the surface. All the settings for the lines in ‘styles’ are turned off except for the uper one ‘edges’.
Could you tell what is happening? Thanks!

kind regards

Rikjan Scholten

So ‘View Hidden Geometry’ is turned off?

Upload the model so others can see what is going on. Just the image doesn’t make things clear.

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Is this something that occurs when you are zoomed further away and disappears when you zoom in? It is due to the graphics engine used in the screen display and can’t be avoided. The lines have a thickness graphically and when you are further away that thickness comes through the surface they are close to.
This will be better when you take the model to LayOut or you output scenes through jpg etc. It is mostly a problem with screen display. You may have to hide some edges for certain views and output.